The present invention relates to processing of compressed video streams, and more particularly to a method of detecting content based defects in a video stream.
Companies which distribute video over compressed pathways, such as satellite or digital cable distributors, have hundreds of channels that need to be monitored for defects. Many choose to use equipment using single ended measurement algorithms, such as that described in co-pending U.S. patent application Ser. No. 09/152,495, filed Sep. 10, 1998 by Bozidar Jenko and Steven Maurer entitled “Picture Quality Measurement Using Blockiness”, for real-time monitoring. However, as these algorithms only measure compression defects, they do not raise alarms based upon the content of the video stream itself. Therefore operators still need to continuously visually examine the channels for content based defects. Such content based defects may include, for example, excessive black or duplicate frames.
Besides blockiness, one of the major forms of defects in large channel distribution streams is “channel starvation.” This typically occurs when an error by an encoder, or the baseband transport from the encoder to the decoder, damages a video stream beyond the decoder's ability to understand it. In this case the decoder has no choice but to repeat a previous frame. Detecting these kinds of errors is a high priority for satellite and digital cable distributors. Unfortunately it is difficult to distinguish channel starvation in a stream from intentional repeat images, such as banners and still frames or freezes. False positives also may occur when detecting SMPTE-A 3:2 pulldown or SMPTE-B 3:2 pulldown from movies at 24 frames per second to NTSC video at 30 frames per second.
What is desired is a robust method of detecting content based defects in a video stream.